In recent years more and more additives such as detergents, pour point depressants, oxidation inhibitors and viscosity index improvers have been employed in petroleum lubricating oils. While these additives have greatly improved the performance of the lubricating oils, they have also greatly increased the task of reclaiming such oils after use. More particularly, resins that normally form in the oil while in use, as well as carbon, dirt, wear metals and other impurities, remain suspended in the oil in the engine by means of modern detergent additives, such as calcium and barium salts of alkyl benzene sulfonic acids, and ashless type detergents, such as alkyl-substituted succinimides. Eventually the suspended impurities are thus largely eliminated from the engine during oil changes and remain within the drained oil.
The economic removal of impurities from used high-detergent lubricating oils, so that the oil may be reused, has proven to be no small task for the reclaimer and is becoming increasingly difficult as more effective detergents are being added to the oils.
Moreover, the modern additive systems have presented a further problem in that such additives must also be removed from the oil stock if the resulting lube oil stock is to be suitable for reformulation to a high-grade lubricating oil.
The purification process used in the past for the separation of carbon and dirt particles from lubricating oils containing no or relatively ineffective detergent additives cannot be satisfactorily used to purify today's high-detergent oils. Since nearly all mineral lubricating oil used today is of the high-detergent variety containing numerous additives, and since service stations tend to place all crankcase drainings into a common tank, practically all used lubricating oil available for re-refining or reclaiming processes has high-detergency properties.
It is an object of this invention to provide a universally applicable system for reclaiming used lubricating oils.
Another object of this invention is to provide an integrated process for reclaiming a high-purity lube oil stock from high-detergent-containing used lubricating oils.
A further object of this invention is to provide an improved process for removing both additives and solid contaminants from used lubricating oils.
Other aspects, objects and the several advantages of this invention will be apparent to one skilled in the art upon study of the disclosure, the claims and the drawings, of which FIGS. 1 and 2 are schematic representations of the process of the invention.
In accordance with one embodiment of this invention, an integrated process is provided which is universally applicable to all used lubricating oils in which the used lubricating oil is contacted with an aqueous solution of an ammonium salt treating agent. Following reaction of the treating agent with ash-forming contaminants of the oil, the bulk of the water phase is removed from the resulting mixture along with any light hydrocarbon, such as gasoline, in the oil. The resulting oil phase is then separated, preferably by filtration, and thereafter subjected to hydrotreating and stripping whereby there is provided a high-grade lube oil stock free of both solids and additive systems. The light hydrocarbon and water mixture is cooled and allowed to separate into a light hydrocarbon and a water layer. The hydrocarbon layer is then pumped to storage and the water layer can be reused in the system.
In accordance with another embodiment of this invention, a method for reducing the ash content of used lubricating oil is provided in which the used oil is contacted with an aqueous solution of an ammonium salt treating agent under conditions such that the ammonium salt treating agent will react with ash-forming metal components present in and entrained in the used oil. Following removal of essentially all of the water and light hydrocarbons present in the reaction mass, the resulting mixture, being essentially free of water, is then separated to provide an oil phase substantially reduced in ash-producing contaminants.
More specifically, in accordance with one embodiment of this invention we have discovered a universally applicable process for removing solid or ash-forming contaminants from used lubricating oils so as to provide an essentially ash-free oil suitable for various industrial purposes which comprises (a) contacting the used lubricating oil with an aqueous solution of a treating agent consisting essentially of an ammonium salt under conditions of temperature, pressure and time sufficient to disperse the agent in the used lubricating oil and to react the agent with the ash-forming components of the used oil; (b) removing a major portion of water from the resulting mixture of used lubricating oil and treating agent from step (a); (c) separating the oil phase from the residual mixture resulting from step (b) and thereafter recovering the resulting oil phase as a product of the process.
In accordance with another embodiment of the present invention, we have discovered a universally applicable integrated process for the reclaiming of essentially all used lubricating oils regardless of the initial additive system contained therein which comprises (a) contacting the used lubricating oil with an aqueous solution of a treating agent consisting essentially of an ammonium salt under conditions of temperature, pressure and time sufficient to disperse the agent in the used lubricating oil and to react the agent with ashforming components of the used oil; (b) removing a major portion of water from the resulting mixture of used lubricating oil and treating agent from step (a); (c) separating the oil phase from the mixture resulting from step (b); (d) subjecting the oil phase to hydrotreating in the presence of hydrogen and a hydrotreating catalyst under conditions of temperature and pressure and time sufficient to produce a hydrotreated oil stock; (e) stripping the resulting hydrotreated oil in a stripping zone and thereafter recovering the resulting hydrotreated lube oil stock as a product of the process.
The used lubricating oils treated by the process of this invention are primarily the discarded oils that have been used for internal combustion lubrication purposes such as crankcase oils, e.g., in gasoline engines or diesel engines. Other sources of used oils include steam-turbine oils, transmission and gear oils, steam-engine oils, hydraulic oils, heat-transfer oils and the like.
The oils used for the purposes named above are the refined lubricating cuts from paraffin-base, mixed-base, or naphthenic crudes. Their viscosities are generally in the range of from about 100 to about 1,800 SUS at 100.degree. F. The oils also contain various additives such as oxidation inhibitors (e.g., barium, calcium and zinc alkyl thiophosphates, di-t-butyl-p-cresol, etc.), antiwear agents (e.g., organic lead compounds such as lead diorganophosphorodithioates, zinc dialkyldithiophosphates, etc.), rust inhibitors (e.g., calcium and sodium sulfonates, etc.), dispersants (e.g., calcium and barium sulfonates and phenoxides, etc.), viscosity index improvers (e.g., polyisobutylenes, poly-(alkylstyrenes), etc.), detergents (e.g., calcium and barium salts of alkyl benzene sulfonic acids) and ashless-type detergents such as alkyl-substituted succinimides, etc.
If desired, water entrained in the untreated used lubricating oil can be removed before use of same in the process of this invention. Such a separation can be readily achieved by removal of the water phase which may occur in the storage tanks for the used lubricating oil.
The ammonium salt treating agents which are useful in the process of the present invention are those selected from the group consisting of ammonium sulfate, ammonium bisulfate, ammonium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, as well as mixtures thereof.
In addition, if desired, precursors of said ammonium salts can be employed instead of part or all of the ammonium salt. Some examples of said precursors include ammonium thiosulfate, ammonium polyphosphates such as ammonium metaphosphate, urea sulfate, guanidine sulfate, urea phosphate, and guanidine phosphate. Other applicable precursors include reactive combinations of ammonia and/or ammonium hydroxide with sulfuric acid and/or phosphoric acid and/or an ammonium hydrogen sulfate or phosphate, i.e., ammonium bisulfate, diammonium hydrogen phosphate, and/or ammonium dihydrogen phosphate. When the precursor comprises a combination of such components reactive with each other to give the desired salt in situ, the components of the combination can be introduced at the same time, or either component can be added prior to the introduction of the other component.
Although the concentration of treating agent in the aqueous solution of treating agent is not critical and more dilute solutions can be used, the economics of the process are enhanced by the use of relatively concentrated solutions in order that the amount of water to be removed subsequently will not be great. Generally the concentration of treating agent in the aqueous solution will be within the range of about 30 to about 95 weight percent, typically about 80 weight percent, of that in an aqueous solution at 25.degree. C. saturated with the treating agent. Frequently some water will be found in used oil, and in these instances the concentration of the treating agent can be adjusted accordingly.
In the process of this invention, the treating agent should be employed in an amount at least sufficient to react with all of the metal constituents in the used oil. Although the weight ratio of the treating agent to the used oil can vary greatly, depending in part upon the nature and concentration of metal-containing components in the oil and on the particular treating agent employed, generally it will be within the range of about 0.002:1 to about 0.05:1, most often being within the range of about 0.005:1 to about 0.015:1, and typically being about 0.01:1. Although larger amounts of treating agent can be used, in most instances this would be wasteful of treating agent.